№489
1) 3 4/15-2 1/8-1/24=49/15-17/8-1/24=49/15-(102-2)/48=49/15-100/48=49/15-25/12=(588-375)/180=213/180=71/60=1 11/60
2) -3-2 2/3-4 5/6+7 1/2=-3-8/3-29/6+15/2=( -36-32-58+90)/12= -36/12= -3
3)1 5/6-2 5/9+4 1/3-3 1/2=11/6-23/9+13/3-7/2=(33-46+78-636)/18=2/18=1/9
4) 0,25-7/12+0,5-1/6=1/4-7/12+1/2-1/9=(3-7+6-2)/12=0/12=0
№490
1) 3,9а-2,81в-5,1а+4,9в= -1,2а+2,09в
2) 1 3/4х-3 7/11у+2 1/4х-5 4/11у=7/4х-40/11у+9/4х-59/11у=4х-9у
3) -1 5/12m-5/7n-7/12m-2/7n= -17/12m-5/7n-7/12m-2/7n= -2m-1n